Bearings

ABSTRACT

A plain bearing is described, the bearing being fitted, in use, in an associated bearing housing, the bearing back in contact with said housing is substantially coextensive with the housing in the axial direction wherein the running surface of the bearing is relieved in both the axial and radial directions so as to reduce the contact bearing surface area with an associated shaft journal, in use.

[0001] The present invention relates to plain bearings and particularly,though not exclusively, engine crankshaft bearings.

[0002] In their widest sense, the characteristics and dimensions of anengine are generally determined by the designer of the engine. Forexample, a four cylinder engine may have either a three or five mainbearing crankshaft intended for it though nowadays, a five bearingcrankshaft would almost certainly be employed. Each engine cylinder willhave a connecting rod which will generally be provided with a bearingcomprising two half shells. The maximum axial length of the bearing willbe determined by the connecting rod thickness (axial length) whichitself will be determined by the space available between the crank websjoining the big-end shaft journals to their adjacent main bearing shaftjournals. Prior art bearings have almost invariably utilised virtuallyall of the possible available length for the provision of the maximumpossible bearing area within the confines of what is available. In somecases, bearing area may be reduced by the provision of oil supply anddistribution grooves and the like.

[0003] Some constructions of so-called flanged main bearings havingintegral thrust washers for controlling crankshaft end-float havenecessarily not utilised all available axial length as bearing area assome available length has had to be sacrificed to allow for attachmentmeans of separate flange members so as to avoid fouling of thecrankshaft in the region of flange attachment. Examples of such bearingsfalling within this category may be found in U.S. Pat. No. 4,989,998 andU.S. Pat. No. 5,267,797.

[0004] U.S. Pat. No. 4,640,630 is concerned with a special bearing for aturbocharger rotor. The bearing described is a floating, generallycylindrical bush-type bearing which rotates both relative to its housingand also relative to the turbocharger shaft which it supports thus, thebearing is not fixed in its housing. Furthermore, the bearing has areduced bearing area in the bore but this is to control the radialstiffness of the bearing which in turn is used to control vibrationsthat can have a detrimental effect on performance in very highrotational speed applications such as turbochargers. Other than givingan optimum range for the ratio of outside diameter length to insidediameter length, no other information is given.

[0005] The reason for maximising the bearing area is to provide as low aspecific load on the bearing as possible during operation of the engine.Minimising the specific load is generally considered to provide otherconsequent bearing benefits such as lower oil operating temperature forany given engine speed and minimum bearing wear for example.

[0006] It is pointed out that in prior art bearings, there are the usualbearing features such as chamfers having corvex curvature, when viewedin section, on the bearing alloy at the bearing end faces which do tendto reduce bearing area by a small amount. However, in general theuniversally accepted bearing design philosophy is to maximise bearingarea, especially on modern highly rated, high-revving engines.

[0007] Thus, in view of the above, it would be surprising if a bearingproduced for a known engine and having a significantly reduced bearingarea compared with that area in the “standard” engine bearing were toproduce a bearing operating temperature lower than with the standardbearing.

[0008] According to the present invention, there is provided a plainbearing, the bearing having a running surface and wherein said runningsurface of said bearing is relieved in both the axial and radialdirections so as to reduce the contact bearing surface area with anassociated shaft journal, in use.

[0009] The plain bearing may be a separate bearing being fitted, in use,in an associated bearing housing, the bearing back being in contact withsaid housing and may be substantially co-extensive with said housing inthe axial direction.

[0010] The plain bearing may be fixed in an associated housing in use,ie the bearing and housing maintain a fixed relationship and do notrotate relative to each other.

[0011] The plain bearing may comprise at least a strong backing materialhaving a bearing alloy lining thereon.

[0012] The relief in bearings according to the present invention may bedistinguished from ordinary chamfers frequently found at bearing ends inthat known chamfers have a convex profile in cross section or a straightline extending directly from the bearing running surface to the outeredge of the bearing axial end face. The relief of bearings according tothe present invention may be considered as a groove or rebate eitherextending to the axial end of the bearing end face or closely adjacentthe bearing end face.

[0013] Bearings according to the present invention have been found toresult in lower bearing running temperatures in spite of the reductionfin bearing surface area.

[0014] When a bearing is assembled into a housing, usually a splithousing wherein each housing half contains a half bearing shell, thereis a nominal clearance between the assembled bearing bore and theassociated crankshaft journal about which the bearing is assembled. Theclearance is to allow for the provision of an oil film to support thebearing and shaft journal in operation. In an engine, a main bearing inthe crankcase is stationary and the rotating crankshaft journal issupported on an oil film whilst a big-end bearing in a connecting rod isdriven by the engine piston and is supported by the shaft journal on anintervening oil film. The clearance allows for maintenance of the oilfilm under conditions where deflection of the bearing in its housing mayoccur and also allows for thermal expansion effects in operation.

[0015] As a factor of the nominal total clearance between the bearingbore and the associated shaft journal, it has been found that the radialclearance may be between a factor of ×2 to about ×15 the nominal totalclearance based on the diameter of the bearing bore and the diameter ofthe shaft journal. For example, if the nominal clearance between bearingand shaft is 0.04 mm then the radial clearance in the relieved portionmay lie in the range from about 0.08 to 0.60 mm.

[0016] The axial length of the relieved portion may be considered as aproportion of the maximum available bearing length which would beavailable without the axial relief. It has been found that an axialrelief ranging from about 5 to about 40% of the available bearing lengthproduces beneficial effects. A preferred range may be from about 10 toabout 30%.

[0017] The relieved portions may be at one axial end of the bearing orat both axial ends. Where the relief is provided at the bearing axialends, it preferable that the relief is disposed substantiallysymmetrically about the bearing length. As an example, if the totalaxial relief is 6 mm then this is preferably provided as two relievedportions each being of 3 mm axial length.

[0018] In some circumstances it is possible that the relief may beprovided within the normal bearing area. However, it is to be understoodthat relief according to the bearing of the present invention is notconstituted by prior art circumferential oil supply grooves. Indeed, thebearing area relieved portions of the present invention are generallyprovided in areas into which oil flows from a remote oil source asopposed to being features into which oil is supplied directly via acrankshaft oil supply drilling for example. Thus the relieved portionsof the bearing of the present invention may receive oil from an oilsupply groove which itself receives oil from a crankshaft oil supplydrilling for example via an intervening portion of the unrelievedbearing surface in the case of an engine main bearing for example. Aconnecting rod bearing on the other hand may be supplied with oil froman oil supply hole in the associated shaft journal, the oil holegenerally being situated about midway between the axial ends of thebearing so that the oil supply is axially outwardly towards the relivedportions.

[0019] It is preferred that the relieved portions are provided in bothhalves of a bearing pair and that the relieved portions arecircumferentially contiguous, i.e. that the relieved portions arecircumferentially aligned in both halves. It is believed that thereshould be no “step” or lack of continuity of the relieved portion at thebearing joint face which would disturb the oil pools or vorticesgenerated at the bearing regions containing the relieved portions. Thus,the relieved portions in one bearing half should blend smoothly with therelieved portions in the adjacent bearing half.

[0020] The reliefs of bearings according to the present invention shouldbe free of obstructions to oil flow.

[0021] Although the relieved portions have been discussed above in termsof separate bearing half shell bearings, the present invention is alsoapplicable to a bearing formed in a connecting rod, for example, whichhas been directly lined with a bearing alloy in the bore thereof such asby high velocity oxy-fuel spraying for example. The present inventionwould apply if axial and radial relief were applied so that not all ofthe available bearing length were lined with the bearing alloy so as toform what would otherwise be a “normal” bearing surface having apredetermined clearance over the whole axial length thereof.

[0022] Similarly, the present invention also applies to substantiallycylindrical sleeve bearings where circular relieved portions may beprovided in the bearing bore.

[0023] The present invention also includes bearings formed for exampledirectly in an aluminium alloy connecting rod. Many small, low-revving,low power engines such as single cylinder engines used in lawn mowersand other horticultural equipment, for example, utilise a directlymachined connecting rod material as the bearing per se.

[0024] Bearings according to the present invention may delay the onsetof so-called bearing touchdown under high power, high speed conditionsdue to the increased oil viscosity stemming from the reduced oiltemperature at a given engine speed.

[0025] It is believed that the reduced bearing operating temperaturesdemonstrated by bearings according to the present invention may be dueto or influenced by turbulence or oil vortices being formed in therelieved portions and which assist in heat transfer from the bearing tothe oil flowing from the bearing.

[0026] The relieved portions may be provided with features which assistin the formation and/or retention of oil vortices to causere-entrainment of oil into the bearing. Such features may comprise lips,for example, formed in or adjacent the relieved portion.

[0027] It is further believed that reduced power loss may be inducedsecondary effects leading to a reduction in bearing operatingtemperature or reduced bearing temperature rise.

[0028] Bearings according to the present invention may compriseconnecting rod big-end or main bearings or any other type of bearing,especially dynamically loaded bearings. However, bearings according tothe present invention may find use in applications other than internalcombustion engines, and examples of such use may include, but are notlimited to: compressors, hydraulic gear pumps, propeller shaft bearingsfor ships and boats and any other bearings which are statically ordynamically loaded.

[0029] In order that the present invention may be more fully understood,examples will now be described by way of illustration only withreference to the accompanying drawings, of which:

[0030]FIG. 1 shows a perspective view of a half bearing according to theprior art;

[0031]FIG. 2 shows a cross section through part of a schematicembodiment of a bearing according to the present invention and anassociated bearing housing and crankshaft journal;

[0032]FIG. 3 shows an enlargement of the detail “A” of FIG. 2;

[0033]FIG. 4 shows a part cross section of a second embodiment of abearing according to the present invention;

[0034]FIG. 5 shows a part cross section of a third embodiment of abearing according to the present invention;

[0035]FIG. 6 shows a part cross section of a fourth embodiment of abearing according to the present invention;

[0036]FIG. 7 shows a part cross section of a fifth embodiment of abearing according to the present invention;

[0037]FIG. 8 shows a part cross section of a sixth embodiment of abearing according to the present invention;

[0038]FIG. 9 shows a part cross section of a seventh embodiment of abearing according to the present invention;

[0039]FIG. 10 shows a graph of bearing temperature rise vs engine speedfor bearings according to the present invention having relieved portionshaving a range of dimensions compared with a “standard” bearing;

[0040]FIG. 11 shows a similar graph to that shown in FIG. 10 but withdifferent test conditions;

[0041]FIG. 12 shows a graph similar to FIG. 10 but with bearingsaccording to the present invention having different dimensionalparameters; and

[0042]FIG. 13 which shows a graph similar to that shown in FIG. 12 butunder different test conditions.

[0043] Referring now to FIGS. 1 to 9 and where the same features aredenoted by common reference numerals. It is to be noted that theembodiments described below are essentially schematic and not to scale.

[0044] A prior art half-bearing for an internal combustion engine isindicated generally at 10 in FIG. 1, the bearing 10 comprises a strongbacking 12 from a material such as steel for example and a bearing alloylining 14 bonded to the backing 12, the lining co-operating, in use,with a shaft journal (not shown). The strong backing 12 may be anythickness from about 0.25 mm upwards. The bearing alloy lining layer 14may be between about 0.25 mm and 1.5 mm in thickness and is frequentlymade from an aluminium alloy or a copper alloy. The bearing 10 may ormay not be provided with a so-called overlay layer of an alloy which issofter than the alloy 14. Such overlay layers are usually in the rangefrom about 15 to 50 μm in thickness, if present. The bearing alloy 14,in the example shown, extends substantially over the whole area of thebearing, i.e. there are no regions where the bearing alloy is cut awayor removed other than at a nick 16 which is provided for axial alignmentin an associated connecting rod.

[0045]FIGS. 2 and 3 show a bearing 20, similar in general constructionto that of the bearing 10 of FIG. 1, installed in a connecting rod 22 ofan engine. The bearing comprises a steel backing 26 having a lining of abearing alloy 28 thereon. Only part of the lower cap-half 24 of the rod22 is shown together with part of the lower half bearing 20. When theconnecting rod is assembled with two half bearings 20, it surrounds acrankshaft big-end journal 30 which is supported between two crankshaftwebs 32, 34. The overall axial length of the bearing 20 is indicated inFIG. 1 as “L”. When the connecting rod 22 and bearings 20 are assembledabout the journal 30, there is a clearance indicated by “d” between thejournal surface 40 and the bearing surface 42, the clearance “d” beingdefined as the difference in diameter between the bore of the bearingformed by the half shells 20 when assembled in the connecting rod 22 andthe diameter of the shaft journal 30. The bearing axis is indicated at44.

[0046] The bearings 20 according to the present invention as shown inFIGS. 2 and 3 are relieved in the bore at their axial ends by theprovision of circumferential recesses 50, 52 which have a dimension “D”in the radial direction and a length “l” in the axial direction. Theenlarged drawing of detail “A” shown in FIG. 3 also indicates a stressrelieving groove 46 formed at the axial end of the shaft journal 30 anda chamfer 48 formed at the end of the bearing receiving bore of theconnecting rod 24.

[0047] The shaft journal 30 has an oil supply hole 36 which, in the caseof the tests described in detail below is supplied with oilindependently and under controlled conditions as described below. Innormal use, the same engine fitted to a vehicle has oil supplied to theoil hole 36 via a drilling in the crankshaft from an adjacent mainbearing. However, the test engine and the normal road use engine bothhave in common the fact that oil is supplied to the bearing at aposition (oil hole 30) such that it flows outwardly towards the relievedportions (as indicated by the arrows 38) to exit the bearing at bothaxial ends thereof to fall into the engine oil pan. Thus, where thereare two relieved portions, one adjacent each bearing axial end, the oilis supplied intermediate the relieved portions to flow through therelieved portions and out of the bearing at the axial ends. This latterconsideration of the relative dispositions of an oil supply hole and therelieved portions applies to all of the embodiments described below.

[0048] In FIGS. 2 and 3, the depth “D” is constant, however, this maynot necessarily be the case as the depth “D” may vary along the axiallength “l”, as will be further described below.

[0049]FIG. 4 shows a second embodiment wherein the relieved portion 52has a lip 60 lying axially outwardly thereof. The total wall thicknessof the bearing is defined as “T” and the thickness of the wall at theposition of the lip 60 is defined as “t” where t< or =T; but, t>(T−D).The axial length of the lip 60 is defined as “m” and may vary accordingto the actual dimensions of the bearing and clearances and with theactual engine application.

[0050]FIG. 5 shows a bearing having a relieved portion of non-uniformdepth. The relieved portion slopes downwardly towards the axial end ofthe bearing at a constant angle. The depth “D” may be defined as theaverage depth from one end to the other of the relieved portion.

[0051]FIG. 6 shows a relieved portion having a reverse slope to thatshown in FIG. 5. Again, the depth “D” may be defined as the averagedepth of the recess from one end to the other.

[0052]FIG. 7 shows a bearing wherein the recess 52 has a curved bottom70. The wall thickness “t” at the outer axial end of the bearing may beequal to or less than “T”. The depth “D” of this recess may be definedas that at the maximum depth of the curved bottom 70.

[0053]FIG. 8 shows a bearing having a stepped relieved portion 72. Theexample shown has three steps, however, there may be more or fewer.

[0054]FIG. 9 shows an embodiment wherein two relieved portions 50, 52are formed axially inwardly of the bearing ends 80, 82. The bearingsurface portions 84, 86 axially outwardly of the recesses are notrelieved in wall thickness and have a thickness “T” as defined above.Tests were conducted with bearings made according to FIGS. 2 and 3having various dimensions of “D” and “l” on a 4-cylinder, in-line, 16valve, double overhead camshaft (DOHC) 2 litre engine having maximumpower at 6000 rpm of 100 kW and maximum torque of 180 NM at 4000 rpm.Engine tests were conducted under the conditions set out in the tablebelow. Engine Test Conditions Engine Speed 3000 4000 5000 5000 6000 6500RPM Enaine Load Full Full Full Min Full Full Full Oil Ternoerature 100 &140 100 & 140 100 & 140 100 & 140 100 & 140 100 & 140 ° C. Oil Pressure2, 3, 4 & 5 At All Speeds bar

[0055] In order to make the tests as representative as possible of thetrue effects of the relieved portions in bearings according to thepresent invention, the engine was modified so that oil under controlledconditions of flow rate, temperature and pressure could be fed directlyto the big-end bearing. In the unmodified engine, oil is normally fed tothe big-end bearings via oil drillings in the crankshaft webs andjournal from the main bearing journals which in turn is supplied withoil under pressure from the integral engine oil pump through a galleryin the cylinder block. However, in the unmodified engine it is notpossible to control the supply of oil to the big-end bearings or tomonitor accurately the change in operating parameters due to thebearings of the present invention. For example, as the engine speedrises, the main bearing has a large effect on the pressure and quantityof oil reaching the big-end downstream thereof such that at high enginespeeds the oil supply in the big-end bearings may cause starvation. Inthe modified testing engine, not only is it possible to accuratelycontrol the input oil parameters as described above but also to monitoraccurately the change in bearing temperature. Oil is introduced into themodified engine via a drilling in the nose of the crankshaft so as toprovide an independent oil feed to the big-end bearing, the normal oilsupply drilling from the main bearing journal to the big-end beingplugged. The oil supply is provided with full-flow meters to monitor oilflow and the bearing 20 being supplied with oil is also provided withthermocouples to monitor change in bearing temperature, thethermocouples (not shown) being positioned about 0.3 mm from the actualbearing surface. Thus, it is the change of bearing temperature which isrecorded rather than oil temperature change. Full details of themodifications to the test engine may be found in the paper: “Measuredcrankshaft bearing oil flow and temperatures with a full and partialgroove main bearing”, by Mian, A. O; Parker, D. D.; Williams, B; SAEpaper OOP-456, March 2000.

[0056] Reference to FIG. 10 shows the results of tests conducted wherethe temperature of the input oil feed is 100° C. at 2 bar. The change inbearing temperature is measured at a range of engine speeds from 3000rpm to 6500 rpm. The bearings were “standard” (1), i.e. those bearingswith which the engine is normally supplied when in a vehicle; bearingshaving relieved portions of 2 mm×0.3 mm deep (2), i.e. “D”=0.3 mm and“l”=3 mm at each axial end of the bearing; 4 mm×0.3 mm deep (3), i.e.“D”=0.3 mm and “l”=2 mm at each axial end of the bearing; 6 mm×0.3 mmdeep (4), i.e. “D”=0.3 mm and “l”=3 mm at each axial end of the bearing;and, 6 mm×0.6 mm deep (5), i.e. “D”=0.6 mm and “l”=3 mm at each axialend of the bearing. In the test engine the radial clearance “d” was 0.02mm giving a diametral clearance of 0.04 mm.

[0057] It may be clearly seen in FIG. 10 that as the dimension “l”increases from 1 to 3 mm at each axial end of the bearing, the bearingtemperature rise (above oil feed temperature of 100° C.) continues todecrease. With an input, oil temperature of 100° C. at 6000 rpm, thebearing having a length “l” of 3 mm at each bearing end and a depth “D”of 0.3 mm according to the present invention has increased intemperature by approximately 26° C. whereas the standard bearing hasrisen in temperature by some 40° C. The effect of increasing dimension“l” from 1 mm to 3 mm at each axial end causes the bearing temperaturerise to continue to fall. The effect of increasing the depth “D” from0.3 mm to 0.6 mm at a dimension “D” of 3 mm at each axial end of thebearing produces a reduction in bearing temperature rise up to 6000 rpmafter which the standard bearing produces a lower increase in bearingtemperature rise.

[0058]FIG. 11 shows a similar graph to that of FIG. 10 except that theoil input temperature is 140° C. rather than 100° C. However, the sametrend as demonstrated in FIG. 5 may clearly be seen in that the depth“D” of 0.3 mm and dimension “l” of 3 mm at each axial end of the bearingproduces the lowest increase in bearing temperature rise across thespeed range until about 6500 rpm when the there is concordance oftemperature rise which is still some 5° C. or more less than thestandard bearing. Again, there is the same trend of lower bearingtemperature rise with increasing dimension “l” up to 3 mm at each axialend of the bearing.

[0059]FIGS. 12 and 13 show graphs of bearing temperature rise forstandard bearings (trace 1) and for bearings having axial end relievedportions of “l”=2 mm and depth “D”=0.1 mm (trace 2). As before, it isclear that the bearings according to the present invention demonstrate areduction in bearing temperature rise at input oil temperatures of both100° C. (FIG. 12) and 140° C. (FIG. 13), the oil supply pressure being 2bar in both graphs.

[0060] Whilst engines may be operated up to high speeds whenaccelerating, an engine in a vehicle spends the great majority of itslife operating at much lower speeds where the effect of the presentinvention is prominent. However, on motorways for example where highsustained vehicle and engine speeds are common, high oil temperaturesare frequently observed especially with the use of cowlings and panelsto improve the aerodynamics of vehicles being common nowadays and whichinhibit the flow of cooling air over the engine oil pan. Consequently,any measures which can be taken to reduce bearing temperatures arebeneficial. Thus, it is to be expected that the life of bearings and theassociated crankshaft may be extended due to lower operatingtemperatures and consequent higher oil viscosity when using bearingsaccording to the present invention.

1. A plain bearing, the bearing having a running surface and whereinsaid running surface of said bearing is relieved in both the axial andradial directions so as to reduce the contact bearing surface area withan associated shaft journal, in use.
 2. A plain bearing according toclaim 1 wherein the bearing is a separate bearing being fitted, in use,in an associated bearing housing, the bearing back being in contact withsaid housing and is substantially co-extensive with said housing in theaxial direction.
 3. A plain bearing according to claim 2 wherein thebearing comprises at least a strong backing material having a bearingalloy lining thereon.
 4. A plain bearing according to either claim 2 orclaim 3 wherein the separate bearing is a half bearing and two suchbearings are fitted in said housing.
 5. A plain bearing according toeither claim 2 or claim 3 wherein the separate bearing is a sleevebearing.
 6. A plain bearing according to claim 1 wherein the bearing isa lining of material deposited directly onto an associated bearinghousing.
 7. A plain bearing according to claim 1 wherein the bearingsurface is formed directly by machining of a housing in which, in use,an associated shaft journal rotates.
 8. A plain bearing according toclaim 7 wherein said housing is an aluminium alloy connecting rod.
 9. Aplain bearing according to any one preceding claim wherein the dimensionof the radial relief is a factor of about ×2 to about ×15 of a nominaltotal clearance between the bearing bore and the associated shaftjournal based on the diameter of the bearing bore and the diameter ofthe associated shaft journal, in use.
 10. A plain bearing according toany one preceding claim wherein the axial length of the relieved portionlies in the range from about 5 to about 40% of the bearing length.
 11. Aplain bearing according claim 10 wherein the axial length of therelieved portion lies in the range from about 10 to about 30% of thebearing length.
 12. A plain bearing according to any one preceding claimwherein the relieved portion has a base parallel to the bearing axis.13. A plain bearing according to any one of preceding claims 1 to 12wherein the base of the relieved portion slopes relative to the bearingaxis.
 14. A plain bearing according to any one of preceding claims 1 to12 wherein the base of the relieved portion is curved.
 15. A plainbearing according to any one of preceding claims 1 to 12 wherein thebase of the relieved portion is stepped.
 16. A plain bearing accordingto any one preceding claim wherein there are two relieved portions. 17.A plain bearing according to any one preceding claim wherein therelieved portion or portions lie at the axial end or ends of thebearing.
 18. A plain bearing according to any one of preceding claims 1to 16 wherein the relieved portion or portions lie inwardly from thebearing axial ends.
 19. A plain bearing according to any one precedingclaim wherein there is a lip axially outwardly of the relieved portion.20. A plain bearing according claim 19 wherein the wall thickness of thebearing at the lip is less than the total wall thickness of the bearingbut greater than the wall thickness at the base of the relieved portion.21. A plain bearing according to any one preceding claim wherein therelieved portions are disposed substantially symmetrically about thebearing length.
 22. A plain bearing according to any one preceding claimwherein the relieved portion or portions extend around the entirebearing circumference.
 23. A plain bearing according to any onepreceding claim wherein, in use, the relieved portions are situatedaxially outwardly of an oil supply hole in the associated shaft journal.24. A plain bearing according to any one preceding claim wherein thebearing is a connecting rod bearing.
 25. A plain bearing according toany one of preceding claims 1 to 23 wherein the bearing is a mainbearing.
 26. An engine having a plain bearing according to any one ofpreceding claims 1 to 25.